Vulcanization of rubber



Patented June 5, 1945 V B. F. Goodrich Company, New York, N. Y., a

corporation of New York No Drawing. Substituted for abandonedapplication Serial No. 487,150, May 15, 1943. This application June 29,1944, Serial No. 542,819

a I 16 Claims. (Cl. 260-788) This invention relates to the vulcanizationof rubber and pertains more specifically to the acceleration ofvulcanization by means of unsymmetrical tertiary amines.

I have previously disclosed, in Patent No. 2,177,548 issued October 24,1939, that certain tertiary amines of the structure (RS-A)3N, where R isan organic radical with the free valence on a carbon atom and A is analkylene group, are efiective accelerators of vulcanization. I have nowdiscovered that tertiary amines of the structure I l V R1SAx A N-A8s RaRr-S-Az where A1, A2, and A3 are alkylene groups and R1, R2, and R3 iseach an organic radical with the free valence on a carbon atom, andwhere not more than two of the R1, R2, and R3 radicalsare identical,give results different from and superior to those obtainedwith theamines previously disclosed by me where all three of the R radicals arethe same.

Although the radicals R1, R2, and R3 of my new amines may be any organicradicals having a free valence on a carbon atom, the preferred classcomprises onlythose amines in which R1, R2, and R3 are members of theclass consisting of 2- thiazyl, Z-thiazolinyl, 2-oxazyl, and2-oxazolinyl radicals. I further prefer the amines in which the radicalsR1, R2, and R3 are all different, although, as stated above, superiorresults may be obtained even when two or them are identical.

' For the sake of convenience I shall designate the aminespreviouslydisclosed by me, in which all three radicals are identical, assymmetrical amines to distinguish them from the unsymmetrical amineshere disclosed.

Theunsymmetrical amines of the present invention may be readily preparedfrom mercapto compounds by the method discolsed in my earlier Patent2,248,356issued July 8, 1941, although any other suitable method mayalso be employed.

Among the unsymmetrical amines which I have found to be excellentaccelerators are the following: methylthiomethyldimethylthiocarbamylthiomethyl ethylthioethyl amine; ethylthiomethylisopropylthioethyl allylthiomethyl amine; cyclohexylthiomethylphenylthiomethyl benzylthi'omethyl amine; o-tolylthiomethylmethylthiomethyl alpha-naphthylthioethyl amine;methylcarbothionylthiomethyl acetylthiomethylethylcarbothionylthiomethyl amine; cyclohexylthioethyl bis(methylcarbothionylthiomethyl) amine; phenylcarbothionylthiomethyldiphenylthiocarbamylthioethyl 3-furoylthiomethyl amine; acetylthiomethylmethylthiomethyl benzy1thioethyl amine; dimethylthiocarbamylthioethylphenylthiomethyl methylcarbothionylthiomethyl amine;diethylthiocarbamylthiomethyl methylethylthiocarbamylthioethylbeta-naphthylthiomethyl amine; ethylthiocarbamylthiomethylmethylphenylthiocarbamylthioethyl ethylthiomethyl amine;diphenylcarbamylthioethyl bis (methylthiomethyl) amine;dicyclohexylthiocarbamylthioethyl diphenylthiocarbamylthiomethyl phenylbeta naphthylthiocarbamylthiomethyl amine; cyclohexylthiomethylacetylthiomethyl diethylthiocarbamylthioethyl amine; acetylthiomethylbis (2-thiazylthiomethyl) amine; dialpha-naphthylthiocarbamylthioethylphenyl-pxenylthiocarbamylthiomethyl dimethylenethiocarbamylthiomethylamine; ethylthiomethyl bis (dimethylenethiocarbamylthioethyl) am i n ephenyl p isopropenylphenylthiocarbamylthioethyl phenyl pdimethylarninophenylthiocarbamylthiomethyl phenylthiomethyl amine;phenylanilinophenylthiocarbamylthiomethyl diphenylthiocarbamylthiomethylmethylethylthiocarbamylthioethyl amine;- dimethylthiocarbamylthioethyl2-thiazylthiomethyl 2-oxazylthiomethyl amine; 2 benzothiazylthioethyl4,5 dimethyl 2 thiazylthiomethyl cyclohexylthiomethyl amine;Z-thiazylthioethyl bis (2-thiazolinylthiomethyl) amine;2-benzooxazylthiomethyl 2-thiazylthiomethy1 2-thiazolinylthioethylamine; 2-benzothiazylthiomethyl Z-thiazolinylthioethyl 4,5 dimethyl 2 ethiazylthiomethyl amine; 2-oxazylthioethyl bis(2-benzothiazylthiomethyl) amine; Z-oxazolinylthioethyl 2-thiazylthiomethyl Z-thiazolinylthiomethyl amine; 2-oxazolinylthioethylbis (4,5-dimethyl-2-thiazolinylthiomethyl) amine; and other similarcompounds.

My new compounds possess the unusual and unexpected property of beingnon-scorching, i. e.

' having no accelerating effect upon the vulcanization of rubber atordinary processing temperatures (about 220 F.), while at the same timebeing highly active at the temperatures usually employd forvulcanization (about 265 to 295 F.). Rubber compositions vulcanized inthe presence of my new accelerators also exhibit remarkably lowhysteresis values and low permanent set as compared with otheraccelerators, for example the symmetrical tertiary amines.

The following specific examples will serve to illustrate the nature ofmy accelerators and their efiect. The following rubber composition wasprepared, in which the parts are by weight:

Rubber 100.0

Soft or semi-reinforcing black 51.5 Laurie acid 3.0 Zinc oxide 10.0Antioxidant 0.75 Sulfur 3.0

Permanent Accelerator set at,

Neither of the above compositions showed any evidence of vulcanizationafter heating 30 minutes at 220 F. There may be compared with theseresults those obtained by employing a symmetrical amine,Z-thiazolinylthioethyl bis (2-thiazolinylthiomethyl) amine, in a similarcomposition. The permanent set of this composition, measured at 212 F.was 18.8%, or 80% higher than the permanent set when accelerator A wasused, and almost 200% higher than when accelerator, B was used. Thiscomposition (C) also vulcanized readily at ordinary processingtemperatures, as is shown by the fact that it exhibited a tensilestrength of 400 lb./sq. in. after heating 30 minutes at 220 F.

The contrast betweenthe symmetrical and unsymmetrical amines is alsostriking in synthetic rubber, as shown by tests on the followingcompositions:

Rubbery copolymer of butadiene and styrene 100.0 Soft orsemi-reinforcing black 50.0 Zinc oxide 10.0 Antioxidant 1.0 Sulfur 2.0

To separate portions of this composition were added 1.75 parts of eachof the following accelerators, per 100 parts of the rubbery copolymer:(D) 4,5-dimethyl-2-thiazylthioethyl-2-thiazolinylthiomethylZ-benzothiazylthiomethyl amine; (E) 2-thiazolinylthioethyl2-thiazolinythiomethyl 4,5-dimethyl Z-thiazylthiomethyl amine; and (F)Z-thiazolinylthioethyl bis (2-thiazolinylthiomethyl) amine. When testedunder the same conditions as the natural rubber compositions describedabove, the' following results were observed:

Permanent Composition set at The unsymmetrical amines were alsonon-scorching in synthetic rubber, as is shown by the fact that when allthree compositions were heated 60 minutes at 220 F. neither (D) nor (E)showed any indication of vulcanization, while (F) had a tensile strengthof 200 lbs/sq. in. The compositions vulcanized with the unsymmetricalamines also exhibitedmuch less heat build-up on flexing than did thecomposition vulcanized with the symmetrical amine; this property isextremely important in any rubber article subject to repeated flexing inuse, particularly in pneumatic tires, because excessive heat tends tocause deterioration of the rubber.

Similar results may be observed when other unsymmetrical amines are usedwith natural and synthetic rubber compositions. The accelerators may beincorporated in the rubber by any of the usual methods, that is, bymixing on a hot' roll mill or in an internal mixer, or by dispersing theaccelerator in the rubber latex, etc. My accelerators are preferablyemployed in amounts ranging from 0.1 to 5.0% by weight of the rubber.There may also be present in the rubber composition any of the usualpigments, fillers, reinforcing agents, dyes, softeners, antioxidants, orother accelerators.

As has been suggested, my new accelerators are effective not only withnatural rubber or caoutchouc, but also with balata, gutta percha,reclaimed rubber, artificial rubber isomers, and synthetic rubbers whichmay be vulcanized with sulfur such as rubbery copolymers of butadienewith styrene, isobutylene, acrylonitrile, methyl acrylate, methylmethacrylate, or the like; the term a rubber as used in the claims isintendedto designate all of the foregoing materials.

Compositions vulcanized with my new accelerators may be used in themanufacture of rubber articles of any description; for example,pneumatic tires and tubes, hose, belting, footwear, molded goods, latexdipped goods, and the like.

Although I have herein disclosed specific embodiments of my invention, Ido not intend to limit myself solely thereto, but only as indicated inwhich A1, A2, and A3 are alkylene groups and R1, R2, and R3 is each anorganic radical with the free valence on a carbon atom, not more thantwo such radicals being identical.

2. The method which comprises vulcanizing rubber in the presence of anamine having the structure R -SAi NAs-SRa R2-S-Az in which A1, A2, andA3 are alkylene groups and in which R1, R2, and R3 is each an organicradical with the free valence on a carbon atom, all three such radicalsbeing different from each other.

4. The method which comprises vulcanizing a rubber in the presence of anamine having the structure NA1s-R.-.

1 R9--SAa in which A1, A2, and A3 are alkylene groups and in which R1,R2, and R3 is each a five-membered heterocyclic radical containing threecarbon atoms, one nitrogen atom, and one chalcogen atom having an atomicnumber less than 17, one

of said carbon atoms being intermediate said nitrogen and said'chalcogen atoms and attached by a double bond to said nitrogen, and thefree valence of said radical being on said intermediate carbon atom, notmore than two of such radicals being identical. 1

5. The method which comprises vulcanizing rubber in the presence of anamine having the structure in which A1, A2, and A3 are alkylene groupsand in which R1, R2, and R3 is each a five-membered heterocyclic radicalcontaining three carbon atoms, one nitrogen atom, and one .chalcogenatom having an atomic number less than 17, one of said carbon atomsbeing intermediate said nitrogen and said chalcogen atoms and attachedby a double bond to said nitrogen, and the free valence of said radicalbeing on said intermediate carbon atom, not more than two of suchradicals being identical.

6. The method which comprises vulcanizing a rubber in the presence of anamine having the structure in which A1, A2, and A3 are alkylene groupsand in which R1, R2, and R3 is each a five-membered heterocyclic radicalcontaining three carbon atoms; one nitrogen atom, and one chalcogen atomhaving an atomic number less than 17, one of said carbon atoms beingintermediate said nitrogen and said chalcogen atoms and attached by adouble bond to said nitrogen, and the free valence of said radical beingon said intermediate carbon atom, all three of such radicals beingdifferent fromeach other. l

7Q The method which comprises vulcanizing a rubber in the presence of4,5-dimethyl-2-thiazylthioethyl 2-thiazolinylthiomethyl2-benzothiazylthiomethyl amine.

8. The method which comprises vulcanizing a rubber in'the presence ofZ-thiazolinylthioethyl Z-thiazolinylthiomethyl4,5-dimethyl-2-thiazylthiomethyl amine.

9. A composition comprising a rubber vulcanized in the presence of anamine having the structure V 1 l in which A1, A2, and A3 are alkylenegroups and 1 R1, R2, and R3 is each an organic radical with the freevalence on a carbon atom, not more than two such radicals beingidentical.

10. A composition comprising rubber vulcanized in the presence of anamine having the structure R1S--A1 N-AaS-Ra RVs-A2 in which A1, As, andA3 are alkylene groups and in which R1, R2, and R3 is each an organicradioal with the free valence on a carbon atom, not

more than two such radicals being identical.

11. A composition comprising a rubber vulcanized in the presence of anamine having the structure in which A1, A2, and A3 are alkylene groupsand in which R1, R2, and R3 is each an organic radical with the freevalence on a carbon atom, all three such radicals being different fromeach other.

12. A composition comprising a rubber vulcanized in the presence of anamine having the structure in which A1, A2, and A3 are alkylene groupsand in which R1, R2, and R3 is each a five-membered in which A1, A2, andA3 are alkylene groups and in which R1, R2, and R3 is each afive-membered heterocyclic radical containing three carbon atoms, onenitrogen atom, and one chalcogen atom having an atomic number less than17, one of said carbon atoms being intermediate said nitrogen and saidchalcogen atoms and attached by a double bond to said: nitrogen, and thefree valence of said radical being; on said intermediate carbon atom,not more than two of such radicals being identical.

l4.- A composition'comprising a rubber Vulcanized in the presence of anamine having thestructu-re in which A1, A2, and A3 are alkylene groupsand in which R1, R2, and R3 is each a five-membered heterocyclic radicalcontaining three carbon atoms, one nitrogen atom, and one chalcogen atomhaving an atomic number less than 17, one

of said. carbon; atoms being intermediate said nitrogen and saidchalcogen atoms and attached by a double bond to said nitrogen, and thefree valence of said radical being on said intermediate carbon atom, allthree of such radicals being different from each other.

15. A composition comprising a rubber vulcanized in the presence of4,5-rdimethyl-2 -thiazylthioethyl 2-thiazolinylthiomethy12-benzothiazylthiomethyl amine.

16. A composition comprising a rubber vulcanized in the presence of2-thiazolinylthioethyl 2- thiazolinylthi'omethyl 4,5-dimethyl-2thiazylthiomethyl amine.

PAUL C. JONES.

